1. Field of the Invention
This invention relates to a brake apparatus for a bicycle, and more particularly to a device for correcting a braking force especially in a region of strong braking force.
2. Description of the Related Art
FIG. 7 shows a conventional roller type hub brake for a bicycle. The hub brake includes a brake drum 1, brake shoes 2 movable into pressure contact with the brake drum 1, a plurality of rollers 3 for pressing the brake shoes 2 upon the brake drum 1, and a brake operating cam 4 for pushing the rollers 3 to press the brake shoes 2 upon the brake drum 1.
The cam 4 is rotatable in a direction of arrow "a" about an axle 7 with an operation of a control arm 5. The cam 4 has inclined surfaces 4a for radially outwardly pushing the rollers 3. As a result, the brake shoes 2 are pressed upon inner surfaces of the drum 1 to apply a braking force thereto.
In the above construction, the drum 1 is rotatable in a direction of arrow "c", opposite to the rotating direction of the cam 4, as the bicycle runs forward. When the braking force is applied with the brake shoes 2 contacting the inner surfaces of the drum 1, the brake shoes 2 are moved by a frictional force in the same direction as the drum 1, i.e. counterclockwise in FIG. 7. With this movement of the brake shoes 2, the rollers 3 also move counterclockwise. Since the inclined surfaces 4a of the cam 4 have a height increasing as they extend counterclockwise, the rollers 3 move radially outwardly as they move counterclockwise, thereby increasing the braking force.
Consequently, the conventional drum brake apparatus applies a greater braking force to the bicycle than a braking force corresponding to an operating force applied to a brake lever not shown. This makes it difficult to effect a fine adjustment of the braking force.